pp.A4-HandOverHandLocking/src/main/java/pp/ThreadsafeSimplifiedList.java

@@ -2,7 +2,6 @@ package pp;
 
 public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   private Node<T> first;
-  private final Object headLock = new Object();
 
   private static class Node<U> {
     U element;
@@ -23,16 +22,16 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
 
   @Override
   public boolean add(T element) {
-    Node<T> curr;
+    synchronized (this) {
-
-    synchronized (headLock) {
       if (first == null) {
         first = new Node<>(element, null, null);
         return true;
       }
-      curr = first;
     }
 
+    Node<T> curr;
+    synchronized (first.lock) {
+      curr = first;
       while (true) {
         Node<T> next;
         synchronized (curr.lock) {
@@ -42,14 +41,17 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
             return true;
           }
         }
+        synchronized (next.lock) {
           curr = next;
         }
       }
+    }
+  }
 
   @Override
   public T get(int index) {
     Node<T> curr;
-    synchronized (headLock) {
+    synchronized (this) {
       if (first == null) throw new IndexOutOfBoundsException();
       curr = first;
     }
@@ -69,7 +71,7 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
   @Override
   public T set(int index, T element) {
     Node<T> curr;
-    synchronized (headLock) {
+    synchronized (this) {
       if (first == null) throw new IndexOutOfBoundsException();
       curr = first;
     }
@@ -90,7 +92,7 @@ public class ThreadsafeSimplifiedList<T> implements SimplifiedList<T> {
 
   @Override
   public boolean isEmpty() {
-    synchronized (headLock) {
+    synchronized (this) {
       return first == null;
     }
   }